1. Field of the Invention
This invention relates to an automated positioning system, as used for placement of integrated circuit devices or components on circuit boards. In particular, the invention relates to the calibration of the apparatus for the system, both at an initial set up and on the change of component, and for other purposes.
2. Related Art
Electronic devices or components are mounted on circuit boards both by the insertion of leads through holes in the circuit board, the holes associated with solder pads, and by surface mounting in which contact leads are positioned on solder pads on the circuit board. In both arrangements, the leads are soldered to the circuit pattern on the board, via the solder pads. As the number of leads per component increases, particularly the increase in the number of leads extending from large scale integrated circuit devices, surface mounting is becoming more widespread. In addition to the increase in the number of leads there is also occurring a reduction in pitch of the leads. From early pitches of 0.1 inches, with the leads being approximately 0.05 inches, pitches of 0.025 inches are now being used with leads of about 0.008 inches. Such leads are very fragile and mounting by insertion of leads into holes is not possible.
As many as 256 leads can be provided on a component, usually positioned around four sides of a packaged component. Contact or solder pads can be formed at a satisfactory degree of accuracy, but consistently positioning a component so that all leads align with pads is very difficult.
Automated positioning machines are widely used for positioning components having less difficult Positioning requirements. Such machines have a high degree of accuracy in repetitive movement. The positioning head can return to a desired position very accurately. However, the components to be positioned are not accurately and consistently positioned at a supply station. This can cause a first element of mispositioning of a component on a circuit board. Because of manufacturing tolerances of circuit boards, circuit boards are not accurately positioned at a loading position. This causes a second element of mispositioning of a component. Inaccuracies in positioning of a component on a circuit board can be along an X axis and/or a Y axis and also relative rotational inaccuracy.